The on-screen display (hereinafter, referred to "OSD") function adopted in the conventional color television refers to such a function that the broadcasting channel, the current time and the like are automatically displayed at a certain position (near the upper or lower edge) of the picture, as well as the data of the received teletext.
Under the OSD mode described above, the color of characters and the background color of the picture should be complementary to each other, so that the information expressed by the characters and figures can be easily recognized by viewers.
Conventionally, however, there has been no circuit for converting the color signals of the on-screen signals, and therefore, the OSD are made either in fixed color, or in the red, green and blue colors in accordance with selected regions.
Accordingly, in the case where the color signals of the main picture and the color signals of the OSD are the same with each other, the OSD can not be distinguished from the background picture video signals.
In order to solve the above described problem, the OSD characters are conventionally surrounded by black boundary lines, however, if the boundary lines are thin, the characters of the OSD can not be easily recognized.
Meanwhile, U.S. Pat. No. 3,911,418 discloses another solution to solve the above described problem, in which the place for displaying the on-screen characters is provided with blocks, and the color of the blocks is varied as against the color of the background of the picture so as to distinguish the characters. However, this has another disadvantage that such a block occupies a considerable portion of the picture.